Acid rain, more properly termed acid deposition, is the input of acidifying compounds from the atmosphere to the earth’s surface. It is comprised primarily of sulfuric and nitric acids that are formed when emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) react in the atmosphere with water, oxygen, and other compounds. Chlorine emissions can also lead to hydrochloric acid, but this usually only accounts for a small fraction of acid rain. The source of sulfur dioxide and nitrogen oxides is principally from the burning of fossil fuels by electric utilities, industries, and motor vehicles. more …